Water activity pigment stability

Isohexides exhibit excellent properties as plasticizers for polyvinyl alcohol polymers.2 Compounds obtained from isosorbide and trialkylaluminum proved to be highly active cocatalysts for polymerization of alkenes. Such derivatives, which were supposed to be oligomeric O-aluminum-isosorbides, are of glass-like appearance and exhibit pyrophoric properties.255 Isosorbide is a component of mixtures used for water-based pigment inks, having excellent dispersion stability, which is necessary for ink-jet printing.256 257... 

Colorants can be divided into water-soluble dyes and water-insoluble pigments. Some of the insoluble colors or pigments can also provide opacity to tablet coatings or gelatin shells, which can promote stability of light-sensitive active materials. Pigments such as the iron oxides, titanium dioxide, and some of the aluminum lakes are especially useful for this purpose. 

COHEN E AND SAGUYI (1983), Effect of water activity and moisture content on the stability of beet powder pigments , J Food Sci, 48, 703-707. 

The most popular method of pigments encapsulation is spray-drying. Many papers present information about microencapsulation by spray-drying, and this method is most frequently used to protect pigments obtained from vegetables, fruits, flowers, and plants, for example, black carrot, curcumin, beetroot, or roselle. Application of natural polymers as shell to protect beetroot color increased the half-life of spray dried dye about three times, whilst pink color was stabile for about 8 weeks. In case of red roselle pigments stabilization, after microencapsulation, it was acceptable to extend the storage time under different water activities up to 4 months. ... 

Investigation of the effects of water activity, salt, sodium metabisulfite, and Embanox-6 on the stability of carotenoids in dehydrated carrots shows that carotenoid pigments were most stable at 0.43a and addition of salt, metabisulfite, and Embanox-6 helped in stabilizing carotenoids in dehydrated carrots (Table 29.9) [71]. 

Decrease of water activity in dry products generally leads to an increase in the half-hfe of these pigments. Maximum stability is observed for a = 0.12. 

Two groups of elements appear in significant concentrations in the original crude oil, associated with well-defined types of compounds. Zinc, titanium, calcium, and magnesium appear in the form of organometallic soaps with surface-active properties, adsorbed in the water-oil interfaces, and act as emulsion stabilizers. However, vanadium, copper, nickel, and part of the iron found in crude oils seem to be in a different class and are present as oil-soluble compounds (Reynolds, 1997). These metals are capable of complexing with pyrrole pigment... 

Note that the spontaneous redispersion of dried particles is a characteristic feature of most sterically stabilized systems, in marked contrast to the behaviour of many (though certainly not all) electrostatically stabilized systems. Note, too, that fresco paints were also produced by dispersing suitable pigments in water. This technology presumably had as one of its antecedents the preparation by Palaeolithic man of cmde paints for cave paintings, an activity that chronologically preceded the preparation of ink in Egypt and China by many millennia. These paints", which were often based on iron oxide, were, however, commonly prepared without a binder. 

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